1. Field of the Invention
The present invention relates to a filtration apparatus comprising semipermeable hollow fibers sealed at one end thereof. A solution to be treated can either be fed to the outside of the hollow fibers and extracted from the inside of the hollow fibers, or fed to the inside of the hollow fibers and extracted from the outside of the hollow fibers in order to remove undesirable components from the solution. The invention relates more particularly to an apparatus in which a bundle of hollow fibers can be simply replaced when they deteriorate or become clogged or destroyed. The present apparatus allows purified water containing no bacteria, pyrogene, or the like to be obtained over a long period of operation.
The invention is described below in connection with an example of an apparatus for purifying water in which undesirable components (such as bacteria) are removed from the untreated water. The apparatus of the present invention can be used for the concentration, purification and recovery of fruit juice, protein and saccharoid, the filtration of aqueous solutions and organic liquids or the treatment of industrial waste water.
2. Description of the Prior Art
A distillation method and a membrane filtration method are known as methods for manufacturing purified water free of bacteria, pyrogene and the like. However, the distillation method has the disadvantages that water purity is reduced by contamination resulting from splashes and bubbles, and contamination also results from dissolution of the materials of the apparatus by heating or other causes.
In the membrane filtration method, although theoretically both bacteria and pyrogene would be removed almost entirely if a membrane which can reject bacteria and pyrogene is used, the treated liquid (hereinafter referred to as "a filtrate") is frequently contaminated with bacteria and pyrogene. In particular, the liquid is often contaminated in extended filtration. The following causes for such contamination are postulated: (1) the membrane itself produces defects; (2) the membrane is incompletely fixed by case molding materials at one end thereof; and (3) the liquid to be treated (hereinafter referred to as "original liquid") leaks into the filtrate because of incomplete sealing of the mechanical sealing materials, such as O-rings, used in the apparatus. Since the quantity of the untreated liquid which leaks into the filtrate is generally very small, it is extremely difficult to find the causes and routes of the contamination. Even if just one bacterium leaks into a filtrate, this bacterium immediately multiplies in the filtrate, thereby contaminating it. In the manufacture of purified water, leakage of original water into the filtrate must be strictly avoided.
Although the leakage of original water into the filtrate from hollow fibers, and from the portions where hollow fibers are collected and fixed rarely occurs as a result of recent rapid advances in the research of membranes (e.g. selective-permeable membranes), leakage of the original water into the filtrate from the mechanical sealing portions of the apparatus is still unsolved. In particular, in an in-line type of filtration apparatus, where an inlet for original water and an outlet for filtrate are arranged in a straight line (a structure which provides easy installation and operation as well as compactness and easy detachability of a bundle of hollow fibers and the like), any leakage of original water from the outside into the filtrate, even from defects in said mechanical sealing portions, cannot be detected. In addition, even though it can be ascertained from a bacterial test of the filtrate that original water has leaked into the filtrate, leakage from mechanically sealing portions cannot presently be distinguished from leakage resulting from defects in the bundle of hollow fibers.